1. Field of the Invention
The present invention relates to a plastic flexible grinding stone for use in removing, by polishing, small protrusions which generate on a coated surface of rolling stocks and industrial machines, as well as in removing stain and oil films from the surface of window glasses.
2. Prior Art
When rolling stocks are placed in parking lots near to railways and iron works, or in places close to construction sites where a coating operation is conducted, iron powder and paint mist fly onto the coated surface of the rolling stocks and adhere thereto to form minute protrusions. Such unfavorable protrusions were conventionally removed by polishing the surface using a compound or a sandpaper.
However, when a compound or a sandpaper is applied to the surface to remove the protrusions, not only the protrusions but also the coated surface are brought into contact with the abrasive to form scratches or flaws on the coated surface. As illustrated schematically in FIG. 3(a), it can be seen that this type of polishing suffers very poor operability, because the abrasive force is fully (100%) exerted on the coated surface if the abrasive force is fully applied to the protrusions.
With a view to ameliorate the poor operability of the conventional method, the present inventor has previously proposed in JP-B-4-11335 (the term "JP-B-" as referred to herein signifies "an examined published Japanese patent application"), a plastic flexible grinding stone comprising a plastic flexible material having mixed therewith fine abrasive such as silica sand and calcium carbonate. When polishing is conducted using the proposed grinding stone, however, as shown in FIG. 3(b) no (0%) polishing force is exerted on the coated surface when the polishing force is fully (100%) applied to the protrusions. Accordingly, it can be seen that a favorable operability is realized for the protrusions, but that the stain cannot be removed from the coated surface.
Conventional grinding stones include plastic flexible ones comprising a plastic flexible material having incorporated therein silica sand and calcium carbonate. The protrusions having formed by adhesion of minute granules or droplets to the coated surface can be removed completely using those grinding stones, however, the stain was left for another means for its removal.